Reactive MnO2 oxides are ubiquitous in the environment, and control the bioavailability and distribution of many toxic and essential elements and organic compounds (Ulrich H J & Stone A T, Environmental Science and Technology 23, 421-428 (1989); Stone A T and Morgan J J, Environmental Science and Technology 18, 450-456 (1984) Stone A T and Morgan J J, Environmental Science and Technology 18, 617-624 (1984) and Tebo B M et al, Annual Review of Earth and Planetary Sciences 32, 287-328 (2004) all of which are incorporated by reference herein). Their formation is thought to be dependent on microbial enzymes, because spontaneous Mn(II) to Mn(IV) oxidation is slow (Hastings D & Emerson S, Geochimica et Cosmochimica Acta 50, 1819-1824 (1986); incorporated by reference herein).
Mn(IV) oxides are recognized as playing an important role in global biogeochemical cycles by linking Mn cycling with other elemental cycles such as S, C, N, P, trace elements and radionuclides through scavenging and oxidation reactions. In the environment, microorganisms are believed to have major control of the formation of Mn oxide minerals. Multicopper oxidases have been implicated as the Mn oxidase in several model Mn-oxidizing bacteria including Leptothrix species, Pseudomonas putida, Pedomicrobium species and diverse marine spore forming Bacillus species whose spores are capable of oxidizing Mn(II) (Corstjens PLAM et al, Geomicroscopy J 14, 91-108 (2009); Geszvain K et al, Applied and Environmental Microbiology 79, 357-366 (2013); Ridge J P et al, Environmental Microbiology 9, 944-953 (2007); Lee Y, Oxidation of Cobalt: Characterization and its Significance in Marine Environments p 159, University of California, San Diego (1994); and Francis C A and Tebo B M Appl and Environmental Microbiology 68, 874-880 (2002); all of which are incorporated by reference herein.)
Several species of marine Bacillus spores oxidize Mn(II) on their exosporium, the outermost layer of the spore, encrusting them with Mn(IV) oxides (Hastings & Emerson, 1986 supra; Francis C A et al, Archives of Microbiology 178, 450-456 (2002); Dick G J et al, Applied and Environmental Microbiology 72, 3184-3190 (2006); Morgan J J, Metal Ions in Biological Systems 37, 1-34 (2000); Nealson K H et al, Adv Appl Microbiol 33, 279-318 (1988); Tebo B M et al, Reviews in Minerology 35, 259-266 (1997); and Bargar J R et al, Geochimica et Cosmochimica Acta 64, 2775-2778 (2000); all of which are incorporated by reference herein.) Molecular studies have identified the mnx (Mn oxidation) genes, including mnxG, a putative multicopper oxidase (MCO), as responsible for this two-electron oxidation (Francis et al, 2002 supra; Van Waasbergen L G et al, Journal of Bacteriology 175, 7594-7603 (1993); van Waasbergen et al, Journal of Bacteriology 178, 3517-3530 (1996); and Dick G J et al, Appl Environ Microbiol 74, 1527-1534 (2008); all of which are incorporated by reference herein).